Plasma membrane is a phospholipid bilayer Protein “icebergs” float in a “sea” of phospholipids
The Cell Membrane
PhospholipidsPhospholipids
Phosphate group Phosphate group forms a forms a hydrophilichydrophilic headhead
Fatty acid tails are Fatty acid tails are hydrophobichydrophobic
Membrane proteins perform a variety of cell Membrane proteins perform a variety of cell functionsfunctions::
Cell Signaling
The Plasma Membrane is The Plasma Membrane is Selectively PermeableSelectively Permeable
What does this mean?What does this mean?
Permeable to:Permeable to:
small molecules, nonpolar small molecules, nonpolar moleculesmolecules
Less Permeable to:Less Permeable to:
charged ions, large molecules, charged ions, large molecules, or hydrophilic moleculesor hydrophilic molecules
What molecules can go What molecules can go directlydirectly through?through?
Carbohydrates?Carbohydrates? No, large & hydrophilicNo, large & hydrophilic
Proteins?Proteins? No, large; many hydrophilicNo, large; many hydrophilic
Lipids?Lipids? Yes; hydrophobicYes; hydrophobicNucleic acids?Nucleic acids? No, hydrophilicNo, hydrophilic
Water?Water? No; hydrophilicNo; hydrophilic
TRANSPORTTRANSPORT
WHY?WHY?
To maintain To maintain HomeostasisHomeostasis
TRANSPORTTRANSPORT
HOW?HOW?
A.A. By Passive ProcessesBy Passive Processes
B.B. By Active ProcessesBy Active Processes
Passive Processes: Passive Processes: DiffusionDiffusion
The movement of moleculesThe movement of molecules
from a region of their from a region of their high high
concentration to a region concentration to a region
of their of their lowlow concentration. concentration.
A drop of food coloring diffuses through gelatin in a petri dish
Figure 8.10 The diffusion of solutes across membranesFigure 8.10 The diffusion of solutes across membranes
Additional TerminologyAdditional Terminology
EquilibriumEquilibrium
Concentration GradientConcentration GradientDifference in concentration Difference in concentration
between 2 regionsbetween 2 regions
All molecules diffuse All molecules diffuse downdown their concentration their concentration gradientgradient
OSMOSISOSMOSIS Special case of Special case of
DiffusionDiffusion1. Movement of Water1. Movement of Water
2. 2. from an area of high from an area of high concentration to an area of concentration to an area of low concentrationlow concentration
3. 3. across a selectively across a selectively permeable membrane.permeable membrane.
Osmosis AnimationOsmosis Animation
Gatorade vs. Gatorade vs. Powerade Powerade
Osmosis LabOsmosis Lab
Solutes and Their EffectsSolutes and Their EffectsHypotonicHypotonicA solution is hypotonic to a second solution if it has A solution is hypotonic to a second solution if it has
less solute dissolved in it than the second solutionless solute dissolved in it than the second solution
HypertonicHypertonicA solution is hypertonic to a second solution if it has A solution is hypertonic to a second solution if it has
more solute dissolved in it than the second solutionmore solute dissolved in it than the second solution
IsotonicIsotonicA solution that has equal amounts of solute as the A solution that has equal amounts of solute as the
second solutionsecond solution
Solutes and Their EffectsSolutes and Their Effects
Water moves from a ________Water moves from a ________
solution to a _________ onesolution to a _________ one
•Water flow equal in both directions
(Equilibrium)
•Net water flow into the cell which can burst
(Hemolysis)
Net water flow out of cell which shrinks(Crenation)
Water Balance in Animal Cells
The contractile vacuole of The contractile vacuole of ParameciumParamecium: an evolutionary adaptation for : an evolutionary adaptation for osmoregulationosmoregulation
PlasmolysisPlasmolysis
Shrinking of cytoplasm due to Shrinking of cytoplasm due to water losswater loss
Plasmolyzed cells become Plasmolyzed cells become FLACCID.FLACCID.
What is the opposite? Swollen What is the opposite? Swollen cells are cells are TURGIDTURGID..
A watered tomato plant regains its turgorA watered tomato plant regains its turgor
Water Balance in Plant CellsRed Onion CellsRed Onion Cells
TurgidTurgid Flaccid Flaccid
Concept GeneralizationsDiffusion:Diffusion: equilibrium, molecules, high equilibrium, molecules, high
concentration, low concentration, concentration, low concentration, passive process, concentration gradientpassive process, concentration gradient
Osmosis:Osmosis: water, passive, high water, passive, high concentration, low concentration, concentration, low concentration, selectively permeable membrane, selectively permeable membrane, hypotonic, hypertonic, isotonic, hypotonic, hypertonic, isotonic, plasmolyzed, flaccid, shrivelplasmolyzed, flaccid, shrivel
Passive transport – diffusion across a selectively permeable membrane
No energy is required. The random movement of molecules move them across the membrane
Facilitated diffusion – specific transport proteins provide a pathway for certain molecules to pass
Is this active or passive transport?
Active transport : ATP (an energy rich molecule) is used to move materials across the membrane against their concentration gradient.
EXAMPLES: 1. Metabolic Pumps: A specific transport protein
pumps solute across a membrane
Example Na+(Sodium) K+(Potassium) pump operates in all cells to maintain charge on the membrane
Figure 8.16 Review: passive and active transport comparedFigure 8.16 Review: passive and active transport compared
Endocytosis – Vesicles form to engulf materials and bring them inside the cell
Exocytosis – spills contents outside the cell
BOTH transport large molecules packaged in vesicles (small membrane sacs)
PhagocytosisPhagocytosisPinocytosisPinocytosis